1. Field of the Invention
The present invention relates generally to a Multiple-Input and Multiple-Output (MIMO) antenna having a plurality of isolation adjustment portions and, more particularly, to a MIMO antenna, which has a plurality of isolation adjustment portions configured to be coupled to a plurality of radiation elements so that they have electromagnetic characteristics different from those of the plurality of radiation elements that operate in multiple frequency bands, thereby improving the isolation in each of the multiple frequency bands in which the plurality of radiation elements operate, and also diversifying the configuration of circuits and the implementation of design.
2. Description of the Related Art
With the recent increasing interest in the fourth-generation communication system capable of high-speed data transmission, related technologies are rapidly developing.
One of the main differences between the four-generation communication system and the previous-generation communication systems is the active adoption of MIMO technology that enables high-speed data transmission.
FIG. 1 is a diagram showing the configuration of a conventional MIMO antenna. As shown in FIG. 1, a plurality of radiation elements 1 and 2 that constitute parts of the conventional MIMO antenna respectively include feeding portions 3 and 4 via which feeding signals flow. Since the conventional MIMO antenna in which the plurality of radiation elements 1 and 2 is arranged and which performs a multiple-input and multiple-output operation is installed in a small-sized mobile communication terminal, the distance between the plurality of radiation elements 1 and 2 should be short. In this case, a problem arises in that the plurality of radiation elements 1 and 2 radiating electromagnetic waves interferes with each other due to current components flowing into the feeding portions 3 and 4 provided in the radiation elements 1 and 2 as feeding signals, and therefore the isolation is so poor as not to ensure high-speed data transmission. In order to overcome this problem, the distance between the feeding portions 3 and 4 included in the plurality of radiation elements 1 and 2 is set to a value equal to or greater than 0.5λ of an operation frequency band so as to improve the isolation in a narrow space. Alternatively, a slit corresponding to 0.25λ of a frequency band which is a target for the improvement of the isolation is formed in a ground surface 5, and therefore the flow of current components is directed to the slit formed in the ground surface 5, thereby reducing the mutual interference between electromagnetic waves radiated by the radiation elements.
However, the former case requires that a distance equal to or longer than a predetermined distance be always ensured, and the latter case prevents parts from being attached to the region of the ground surface where the slit is formed. Accordingly, both the cases have the problem of not being flexible in terms of the configuration of circuits and the implementation of design.
Although to solve the problem, technology for improving isolation by directing current components that influence feed points provided in a plurality of radiation elements to an isolation device using coupling was proposed, this technology has the problem that with regard to the radiation elements operating in multiple frequency bands, the improvement of isolation in a low frequency band is significantly greater than that in a high frequency band, and therefore there is a great difference in the improvement of isolation between individual frequency bands.
Accordingly, there is a pressing need for MIMO antenna technology that can uniformly improve isolation in all of the multiple frequency bands in which radiation elements operate and that can allow the configuration of circuits and the implementation of design to be diversified.